Is it permissible for a mother to divide her gold among her children and allocate a portion of it to her granddaughters (daughters of her son), knowing that she designated one portion to be divided exclusively among her daughters, and another portion to be divided among all her children? And what is the meaning of: "No will for an heir"?

Bequesting some gold to daughters and the son (heirs) is a non-binding will and is not executed except with the consent of all heirs. As for bequests to the son's daughters (non-heirs), they are considered valid and binding up to one-third of the estate. If it exceeds one-third, the consent of the heirs is required for the excess. A condition for the validity of an heir's consent is that they must be an adult of sound judgment.